1. Field of the Invention
The present invention relates to a magnetic head which performs recording or reproduction of information signals on a magnetic recording medium, a method for producing the same, and a magnetic recording/reproduction apparatus using the same. It relates particularly to a narrow-track magnetic head for high density magnetic recording used in a digital VCR or the like, a method for producing the same, and a magnetic recording/reproduction apparatus using the same.
2. Description of the Related Art
In order to record/reproduce a large amount of information signals such as found in digital VCR, it is necessary to employ high density magnetic recording/reproduction techniques such as the narrow-track technique and the short-wavelength technique. Generally, it is known that for the realization of high density magnetic recording/reproduction, it is better to increase the coercive force of a recording medium or to increase the saturation magnetic flux density (hereinafter, referred to as a xe2x80x9cBsxe2x80x9d) of a magnetic head.
However, a ferrite material, which has mainly been used in the prior art as a material for a magnetic head, has a Bs of about 0.5 T, which is not sufficiently large. Therefore, when a prior art magnetic head made of the ferrite material is used on a metal tape having a high coercive force of 80 kA/m or more, there occurs magnetic saturation so that a recording and reproduction of information might not be conducted with certainty.
To resolve the situation, magnetic heads have currently been suggested which are made of a new material having a Bs larger than that of the ferrite material, such as a Sendust alloy film (Bs: about 1.0 T) or a Co type amorphous film (Bs: about 0.8 T to about 1.1 T), or other materials having a Bs of about 1.3 T or more, such as a Co type superstructure nitriding alloy film, an Fe type superstructure nitride film or an Fe type nitride film. Among these, research has been vigorously conducted particularly on a composite magnetic head, or so-called MIG head, in which the main core is made of ferrite and a magnetic thin film is disposed on the surface of the main core at least in the vicinity of the front gap.
FIG. 13 is a perspective view illustrating an example of a configuration of a prior art MIG head.
In the prior art MIG head 500 shown in FIG. 13, a pair of convex or bevelled magnetic cores 502 and 503 are disposed opposite to each other with a magnetic gap 501 being therebetween. The magnetic core 502 includes a convex or bevelled core body 504 (hereinafter, simply referred to as the xe2x80x9ccore body 504xe2x80x9d) made of ferrite and a magnetic film 506 which is formed on the surface of the core body 504 and has a high saturation magnetic flux density. Similarly, the magnetic core 503 includes a convex or bevelled core body 505 (hereinafter, simply referred to as the xe2x80x9ccore body 505xe2x80x9d) made of ferrite and a magnetic film 507 which is formed on the surface of the core body 505 and has a high saturation magnetic flux density. The magnetic films 506 and 507 are formed so as to cover the projection end faces of the core bodies 504 and 505, respectively, facing the magnetic gap .01, and also completely cover both of the side faces therefrom. The magnetic gap 501 is provided with a nonmagnetic film (referred to as xe2x80x9cgap memberxe2x80x9d) not shown in FIG. 13. The magnetic cores 502 and 503 are butted to each other with the magnetic gap 501 including the gap member inserted therebetween. Furthermore, the magnetic cores 502 and 503 butted as such are coupled to each other with a pair of glass blocks 508 and 509 which are disposed at both sides of their butting ends. A winding window 510 for coils to pass is provided at the middle of the side faces of the MIG head 500.
In view of the narrow-track technique, the MIG head 500 described above may not be formed with sufficient accuracy with respect to a track width due to a production error such as butting accuracy of the two magnetic cores 502 and 503, or due to the influence of a roundness at the track edge of the magnetic films 506 and 507. Moreover, since the track width cannot be determined unambiguously, sufficient accuracy may not be obtained during the adjustment steps for the track height during assembly. Consequently, a decrease in the yield may result in the production of the MIG head 500.
In order to solve these problems, the applicant of the present application has suggested an MIG head as disclosed in Japanese Laid-Open Patent Publication No. 7-220218, which corresponds to pending U.S. patent application Ser. No. 08/313,594 filed on Sep. 29, 1994. In FIG. 14, a configuration of the top face of the MIG head 600, i.e., the sliding surface for a magnetic tape, is schematically illustrated.
A fundamental configuration of the MIG head 600 is similar to that of the MIG head 500 described before. A pair of convex or bevelled magnetic cores 602 and 603 are disposed opposite to each other with a magnetic gap 601 being therebetween. The magnetic core 602 includes a convex or bevelled core body 604 (hereinafter, simply referred to as the xe2x80x9ccore body 604xe2x80x9d) made of ferrite and a magnetic film 606 which is formed on the surface of the core body 604 and has a high saturation magnetic flux density. Similarly, the magnetic core 603 includes a convex or bevelled core body 605 (hereinafter, simply referred to as the xe2x80x9ccore body 603xe2x80x9d) made of ferrite and a magnetic film 607 which is formed on the surface of the core body 605 and has a high saturation magnetic flux density. The magnetic films 606 and 607 are formed so as to cover the projection end faces of the core bodies 604 and 605, respectively, facing the magnetic gap 601, and also completely cover both of the side faces therefrom. The magnetic gap 601 is provided with a nonmagnetic film as a gap member. The magnetic cores 602 and 603 are butted to each other with the magnetic gap 601 including the gap member inserted therebetween. Furthermore, the magnetic cores 602 and 603 butted as such are coupled to each other with a pair of glass blocks 608 and 609 which are disposed at both sides of their butting ends.
The magnetic tape sliding face of the MIG head 600 is provided with notches 613a and 614a over both of the magnetic cores 602 and 603 in addition to a convexly processed part 639 which regulates the track width. By having these notches 613a and 614a, a track misalignment associated with the butting accuracy of the magnetic cores 602 and 603 within the magnetic head 600 is eliminated, and degradation of accuracy due to a roundness of the track edge, or so-called fringe, is also reduced considerably.
However, since a number of processes are also conducted after processing steps for the notches 613a and 614a in the production of the MIG head 600, there may result a track misalignment between the magnetic cores 602 and 603 on a microscopic level, and it may be the case that an initial track width cannot be maintained with sufficient accuracy.
Furthermore, the side faces of the convexly processed or bevelled part 639 of the magnetic cores 602 and 603 are provided with an antireaction film 640 made of a material such as SiO2, ZrO2, Ta2O5, glass, Cr, or a composite thereof, at the interfaces between the glass blocks 608 and 609 and the magnetic films 606 and 607. Thus, a chemical reaction between the magnetic cores 602 and 603 (more precisely the magnetic films 606 and 607) and the glass blocks 608 and 609, respectively, is inhibited. However, the interfaces between the magnetic films 606 and 607 and the glass blocks 608 and 609 at the notches 613a and 614a are not provided with such antireaction films 640. Consequently, the chemical reaction may occur therebetween and, as a result, problems such as a blur at the track edge may occur.
Due to problems described above, even with the MIG head 600 illustrated in FIG. 14, problems associated with the accuracy of the track width still remain.
On the other hand, improvement of the accuracy of the track width has been tried in several prior art techniques so far.
For example, U.S. Pat. No. 4,110,902 discloses a method for regulating a track width by a wire from the top face of the sliding face. This is to process the entire sliding face for a fixed track width. However, a problem concerning wear resistivity due to contact with a running magnetic medium may result, and there is a possibility of significant deterioration of magnetic characteristics.
U.S. Pat. No. 3,668,775 discloses a magnetic head which is configured such that a dimension of the this entire core matches the track width. However, even with this configuration, there is still a possibility of significant deterioration of magnetic characteristics. Moreover, strength of the magnetic head may deteriorate.
Furthermore, U.S. Pat. No. 5,298,113 discloses a production method for a magnetic head in which the vicinity of a track is processed with a turning tool. In this method, however, there is a possibility that an edge of the magnetic gap, which is a primary part of the magnetic head for conducting magnetic recording/reproduction, is damaged. An occurrence of such damage leads to a deterioration of magnetic characteristics and is not preferable in view of operational characteristics of the magnetic head. Moreover, in view of machining accuracy, it is difficult to process with an accuracy of about 1 xcexcm or less. Particularly, there is a difficulty in keeping constant machining accuracy in the depth direction of the magnetic gap.
Furthermore, in the disclosed machining method using the turning tool, the turning tool must be pressed against the magnetic core to process it into a predetermined shape during actual implementation of the method. As a result, materials in a bar shape cannot be processed, posing a problem associated with the realization of mass production. In addition, a deterioration of magnetic characteristics may occur due to a process-induced denatured layer on the processed surface, posing a problem that a predetermined effective track width cannot be maintained with accuracy.
As a result of the recent improvement of a recording density in magnetic recording, it is becoming a requirement that, for a magnetic head, a track width of about 10 xcexcm or less be obtained with an accuracy of about xc2x10.5 xcexcm or less. However, as has been described above, it is almost impossible with the prior art technique to meet the requirements described above without a deterioration of magnetic characteristics.
The magnetic head according to the present invention includes: a pair of magnetic cores each having a convexly processed part, said convexly processed parts being disposed opposite to each other with a magnetic gap member inserted therebetween; and a pair of glass blocks disposed on both sides of said pair of magnetic cores, thereby coupling together said pair of magnetic cores. A magnetic film is formed at least on a projection end face of said convexly processed part in each of said pair of magnetic cores; and a pair of notches regulating a track width are formed on a magnetic tape sliding face of said pair of magnetic cores by electric discharge machining so as to flank a butted part of said convexly processed parts of said pair of magnetic cores from both sides, said pair of notches having a shape such that an interface thereof is not positioned out of an edge of a recording pattern on a magnetic tape when said magnetic tape travels.
Preferably, said pair of notches are circular in shape. More preferably, a tangent to an arc of said notch at an intersection point of a magnetic gap and said arc is substantially parallel with a direction of travel of said magnetic tape. Alternatively or further preferably, a radius of the arc of said notch is smaller than a minimum thickness of said magnetic film provided on said projection end face.
In one embodiment, an interface between said magnetic film and said magnetic core is substantially parallel with a face of said magnetic gap at said projection end face.
Preferably, an antireaction film is further provided at least between said pair of notches and said pair of glass blocks.
Preferably, each of said pair of glass blocks includes a front glass block positioned close to said magnetic tape sliding face of the magnetic head and a back glass block positioned away from said magnetic head sliding face. A softening point of said front glass block is set lower than a softening point of said back glass block.
According to another aspect of the invention, a magnetic head includes: a pair of magnetic cores each having a convexly processed part, said convexly processed parts being disposed opposite to each other with a magnetic member inserted therebetween; and a pair of glass blocks disposed on both sides of said magnetic cores, thereby coupling together said pair of magnetic cores. A magnetic film is formed at least on a projection end face of said convexly processed part of at least one of said pair of magnetic cores. A pair of notches regulating a track width are formed on a magnetic tape sliding face of said pair of magnetic cores so as to flank a butted part of said convexly processed parts of said pair of magnetic cores from both sides. And an antireaction film is provided at least between said pair of notches and said pair of glass blocks.
According to still another aspect of the invention, a magnetic head includes: a pair of magnetic cores each having a convexly processed part, said convexly processed parts being disposed opposite to each other with a magnetic member inserted therebetween; and a pair of glass blocks disposed on both sides of said magnetic cores, thereby coupling together said magnetic cores. A magnetic film is formed at least on a projection end face of said convexly processed part of at least one of said pair of magnetic cores. A pair of notches regulating a track width are formed on a magnetic tape sliding face of said pair of magnetic cores so as to flank a butted part of said convexly processed parts of said pair of magnetic cores from both sides. And each of said pair of glass blocks includes a front glass block positioned close to said magnetic tape sliding face of the magnetic head and a back glass block positioned away from said magnetic head sliding face, a softening point of said front glass block being set lower than a softening point of said back glass block.
In the magnetic head having the aforementioned configurations, said notch is preferably formed by electric discharge machining.
Preferably, each of said pair of magnetic cores includes a ferrite core, said magnetic film being provided on a surface of each of said ferrite core, and said pair of notches being formed only in said magnetic film.
In one embodiment, the magnetic head further includes a winding window for winding a coil, said pair of notches reaching said winding window.
According to the present invention, a magnetic recording/reproduction apparatus which includes a magnetic head having the aforementioned configurations is provided.
According to still another aspect of the invention, a method for producing a magnetic head is provided, wherein said head includes: a pair of magnetic cores each including a convexly processed part and a magnetic film provided at least on a projection end face of said convexly processed part; and a glass block including a front glass block positioned close to a front. face of said magnetic core and a back glass block positioned away from said front face of said magnetic core. The method includes: the first step of disposing said projection end faces butted to and opposite to each other with a magnetic gap member inserted therebetween; the second step of providing, by electric discharge machining, a pair of notches regulating a track width on a magnetic tape sliding face of said pair of magnetic cores so as to flank a butted portion of said convexly processed part of said pair of magnetic cores from both sides; the third step of forming an antireaction film preventing chemical reaction between said metal magnetic film and said glass block at least on a surface of said pair of notches; and the fourth step of filling with a glass material a groove provided beforehand at a predetermined position of said pair of magnetic cores by heat treatment so as to form said front glass block.
Preferably, the method further includes the step of welding together said pair of magnetic cores with said back glass block prior to the formation of said notch.
According to still another aspect of the invention, a method for producing a magnetic head is provided, wherein said head includes: a pair of magnetic cores each including a convexly processed part and a metal magnetic film provided at least on a projection end face of said convexly processed part; and a glass block including a front glass block positioned close to a front face of said magnetic core and a back glass block positioned away from said front face of said magnetic core. The method includes: the first step of disposing said projection end faces butted to and opposite to each other with a magnetic gap member inserted therebetween; the second step of welding together said pair of magnetic cores with said back glass block; the third step of providing, by electric discharge machining, a pair of notches regulating a track width on a magnetic tape sliding face of said pair of magnetic cores so as to flank a butted portion of said convexly processed part of said pair of magnetic cores from both sides; and the fourth step of filling with a glass material a groove provided beforehand at a predetermined position of said pair of magnetic cores by heat treatment so as to form said front glass block.
Preferably, a softening point of said front glass block is set lower than a softening point of said back glass block, and a heat treatment temperature in the step of forming said front glass block by thermal filling is set lower than the softening temperature of said back glass block.
Preferably, in the step of forming said notch by electric discharge machining, an end portion of said magnetic core is machined by an electric discharge machining electrode of a cylindrical shape while rotating the electrode.
In one embodiment, in the step of forming said notch by electric discharge machining, an end portion of said magnetic core is machined with a tip of an electric discharge machining electrode reaching at least a winding window.
According to the present invention, a magnetic recording/reproduction apparatus which includes a magnetic head formed by a production method described above is provided.
Thus, the invention described herein makes possible the advantages of (1) providing a high performance narrow-track magnetic head which can be used for high density technique for magnetic recording, (2) providing a method for producing the above-mentioned narrow-track magnetic head with a high yield and at low cost, and (3) providing a magnetic recording/reproduction apparatus suited for a narrow-track pitch by utilizing the above-mentioned magnetic head and the production method thereof.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.